Coating for stereotype matrices



Patented Sept. 25, 1934 UNITED STATES 1,974,477 COATING roa STEREOTYPEMATRICES Louis G. Walters, New York, N. Y., assignor to ElcctrographicCorporation, New York, N. Y., a corporation of Delaware No Drawing.Application June 1933, Serial No. 675,971

6 Claims.

The present invention relates to a coating for the facing surface of astereotype mat.

Stereotype mats are a special type of paper board and are sufficientlyplastic to receive impressions from printing faces when the matrix boardis pressed under substantial pressure against type or other printingfaces. The impressed matrix board is then used as a mold face againstwhich molten type metalis poured to form a stereotype printing plate.The texture of the surface of the matrix board is relatively coarse anddoes not produce a smooth printing surface. Furthermore, the fibrousmaterial of which the matrix board is composed tends to burn out whensubjected to a number of casts from hot type metal.

The present invention overcomes the difficulties of the known prior artby providing a surface coating on the matrix board, which coating willmold into the finest lines on half tones or type and is of such texturethat the coating molds as a smooth surface against the smooth type face.

Furthermore, my new coating is of such material as to withstand the heatof molten type metal so that a number of casts may be made from a singlematrix board.

Coatings for matrix board have heretofore been suggested but thesecoatings have been unsuccessful because of materials used in the coatingproducing undesirable and deleterious effects. It has been proposed touse binders in coatings which binders melt when subjected to heat andwhich binders tend to gasify when subjected to the heat of molten typemetal. Such binders introduce several dimculties. It is customary toheat the type or plates from which the stereotype mat is made andcoatings having binders which melt tend to stick to the heated type.Where such mats are used against cold type, the chief difflculty ispostponed until the melted type metal strikes the mat when the binderfirst melts and then gasifles, thereby producing a very rough surface.The coating also tends to stick to the molded stereotype plate and thusthe matrix is destroyed when the matrix board is removed from thestereotype plate.

A still further and important attribute of a coating for a stereotypeplate is that the coating must be extremely flexible and rubber-like atthe time when the matrix board is forced under pressure against the typeand printing faces. The coating must not shrink to any substantialextent when it dries out, otherwise it will distort the matriximpressions.- Unless the coating is flexible and capable of stretching,it will break over the edges of the type faces and form small cracks.When the molten type metal is cast against a cracked matrix, the metalflows intothese cracks and interlocks with the coating. This tears awaya part of the matrix surface when the matrix board is removed from thecast plate.

The present invention overcomes the difiiculties of the known prior artand in actual use has demonstrated that it is a practical commercialproduct comprising a substantial improvement in the art.

The present coating comprises the use of colloidal-graphited water (soldunder the trade name of Aquadag) mixed with distilled water and potatostarch. The preferred formula is ten ounces of Aquadag plus four ouncesof potato starch, added to one gallon of luke warm distilled water. Thematerials are thoroughly mixed and when so mixed will stand forsubstantial lengths of time without any change or deterioration.Preferably, the coating material is heated to luke warm temperature orapproximately 100 F. and then is applied to one face of the matrixboard. The coating may be applied by so brushing the surface of theboard with the liquid coating or by spraying the coating on the board inthe usual manner of spraying paint materials.

Preferably, two coats of the material are applied to the matrix board.The first coat acts as a prims5 ing coat and soaks into the matrixboard. In a seven ply matrix board, the coating appears tosoak throughsubstantially three plies. This first coat is permitted to dry and thena second coat is laid on in the same manner as the first coat. Thesecond coat forms a perfect bond with the first coat and layssubstantially entirely upon the surface so as to form a surface layer ofgraphite and potato starch after'the carrying medium, namely, the water,has been dried out. Other starches have been tried such as corn starch,or a wheat starch, but potato starch seems to be the most satisfactoryin that it is finer and lighter than other forms of starch. Itremains-in solution and also produces a very fine grain coating on thesurface of the matrix board when the coating has dried.

The coated sheet may be used as a so-called dry mat, or as a wet mat.Preferably, it is used as a wet mat and when so used, it is desirable tomoisten the back of each sheet with a sponge soaked in water. Then, thesheets are piled back to back and face to face, and after fifteenminutes time are ready for use. The surface coat at this time is of arubbery consistency and will 110 bend and stretch without breaking. Thematrix board is applied with coated side toward the type or plates fromwhich the mold is to be made. The type or plates are preferably heatedto about 150 F. and thematrix boardis pressed against the printingfaceswith a substantially heavy pressure sufficient to impress the type facesinto the coated surface. This pressure may be quickly released and thenthe type with the matrix board resting thereon may be moved to a steamtable and subjected to lighter pressure for two or three minutes whichis sufficient time to completely drive out the moisture from the mat andthe mat is then ready for use as a stereotyping mat. This new coatingdoes not shrink seriously when drying and does not pull or producedouble impressions as is the case where the prior art coated mats arepressed and the pressure released and re-applied.

The matrix board is now ready for use, and may be used with highertemperatures than other matrix boards heretofore used in the art.Preferably, applicants matrix is used with type metal heated to about800 F. and even with this high temperature, many stereotype plates maybe made from a single matrix without burning or destroying the matrix.

Applicants matrix requires no face treatment as is common in the art ofstereotyping. Usually, stereotype matrices are coated with Frenchv chalkor zinc stearate or other face treatment compounds. In this new mat, theface as it leaves the printing type is ready for immediate use with outfurther treatment of any kind.

The coating on the novel mat herein described adheres very tightly tothe face of the matrix board and does not tend to chip or peel off. Whenthe mat has been pressed against the type, the impression surfacespresent a bright polished appearance which is retained during thesubsequent use of the mat.

What I claim is:-

1. The process of preparing a matrix board for stereotyping comprisingapplying to a surface of said board as a coating a solution ofcolloidalof colloidal-graphited water and starch suspended in water;permitting the priming coat to soak into said board; drying the primingcoat; applying a cover coat of said graphite, starch, and water solutionto form a layer of finely divided graphite and starch covering a surfaceof said board; and drying off the excess water from said cover coating.

3. An article of manufacture comprising a ma trix board for stereotypinghaving a surface thereof covered with a coating of very finelydividedgraphite deposited from a colloidal graphited water solution and starchparticles.

4. An article of manufacture comprising a matrix board for stereotypinghaving a face thereof impregnated with a water solution of very finelydivided graphite and starch, and with a layer of impregnating materialforming a covering surface of graphite and starch overlying a face ofthe said board.

5. An article of manufacture comprising a matrix board for stereotypinghaving a surface thereof covered with a coating comprising a mechanicalmixture of very finely divided graphite and potato starch, said coatingbeing of sufiicient thickness and depth to completely cover the fibersof said board whereby the coating receives the impression when saidboard is used for stereotype molding.

6. An article of manufacture comprising a matrix board for stereotypinghaving a surface thereof coated with finely divided graphite depositedfrom a colloidal graphited water solution and potato starch, thegraphite and potato starch being substantially in the proportions byweight of ten percent wet graphite with four percent dry starch.

LOUIS G. WALTERS.

